High-capacitance, long-service life capacitors are required of late. Electric double-layer capacitors offer very high output, but their energy density is low; on the other hand, batteries offer high energy density but their output is low. In more applications, batteries are being replaced by lithium ion capacitors using lithium-occludable material for the negative electrode, because lithium ion capacitors offer higher energy density than electric double-layer capacitors and longer service life than batteries.
On the other hand, lithium ion capacitors require the so-called “pre-doping” step where lithium ions are doped into the negative electrode, which leads to low productivity. In the manufacturing process for lithium ion capacitors described in Patent Literature 1, for example, the electrodes must be cut so that lithium can be placed in the device, after which the lithium must be connected by welding.
Also, Patent Literature 2 discloses a lithium ion electric storage element constituted by a negative-electrode collector on which an active material layer is stacked, wherein a region where the active material layer is not stacked is formed on the negative-electrode collector, and lithium is placed in this region for pre-doping.